One advertiser noticed he has received 1,201,660 clicks, costing him $965,212.38!

Yea, almost $1 million for just over 1 million clicks.

What happened? It appears that Yahoo upgraded the reporting features amongst other things, which caused some advertiser's reports to show huge spikes in numbers.

I would not panic, it appears to be a reporting issue only and there are no confirmed reports of actual charges of $1 million being placed on any advertiser's credit card. In fact, one advertiser reported that Yahoo is already fixing the issue.

I emailed my Rep & he said they know about it & they are working on resolving it already. The UI was upgraded & there are quite a few bugs that were produced because of it. We can't log into some accounts from certain countries at all now.